The present invention relates to an atomizing pump especially for water solutions, as well as to a method of manufacturing the same. Such pumps are utilized in cosmetics and pharmaceutic fields for dosed atomization and application of liquid preparations.
Atomizing pumps which are presently used are of different constructions. All these constructions have a common characteristic feature which includes a pressure chamber provided inside a stationary cylinder and having a variable volume by a longitudinally displaceable piston. The piston seals the pressure chamber at the cylinder wall by at least one sealing sleeve lip. It performs a predetermined by design, reproducible displacement stroke and is automatically returned to its initial position by a pressure spring. The pressure chamber is limited at the aspiration side by an inlet valve which operates automatically during pressure application or forcibly in dependence upon the pressure stroke. At the outlet side the pressure chamber is limited by an outlet valve which operates in dependence upon pressure or path and is arranged in the region of the piston or in a subsequent structural part. An extraction head is located after the outlet valve and is connected by a hollow piston shaft with the pressure chamber. In dependence upon its construction, the extraction head atomizes the fluid. A riser pipe is connected with the inlet valve and extends inwardly to a bottom of the container. Withdrawal of the liquid is performed by application of pressure to the piston via the extraction head in such a way that the inlet valve closes, the outlet valve opens, and the liquid with a downward displacement of the piston is discharged until the end position is attained. During return displacement of the piston with the closed outlet valve, the pressure chamber is again filled with liquid via the opened inlet valve. An advantageous construction of this pump is the pressure atomizing pump in which the opening of the outlet valve is performed first with formation of a predetermined minimum liquid pressure in the pressure chamber of usually approximately 5 bar, whereby a positive uniform atomization substantially independent from the actuating force is produced.
The above described atomizing pumps are manufactured in great quantities as mass articles and composed, with the exception of the pressure spring and eventually a ball, exclusively of synthetic plastic parts. These parts are produced by injection molding in a multiple tools from thermoplastic synthetic plastic materials and assembled in subsequent working steps by assembling automatic machines to an end product. A relatively great tolerance play is required in such a mass production. This play is compensated for in the sealing region between the cylinder and the piston in that the provided sealing lip of the piston is oversized relative to the maximum possible inner diameter of the cylinder. The already unfavorable friction coefficient of the plastic parts relative to one another is increased by the oversize which increases the prestress. Thereby actuation of the pump with a possible actuation force, as well as automatic return stroke of the piston to the initial position, are not possible without an additional lubrication of the mutually sliding surfaces. Because of this, during mounting of the pump, the plastic parts are supplied with a small quantity of lubricating medium which reduces the adherence and friction. Particularly silicon oil is used for this purpose since, in addition to physiological acceptability and good creep properties, it is suitable because the formed lubrication film is both mechanically and chemically resistant and is not released by the atomizing liquid from the sliding surfaces. It is retained during the atomization of great liquid quantities to the full emptying of the pack and thereby operational failures of the pump, for example by seized piston, are prevented. Similarly to the synthetic plastic parts formed mainly on polyolefin basis, the silicon oil also exhibits essential hydrophobic properties. These hydrophobic properties in the event of atomization of non-water solutions do not lead to the disadvantageous phenomena or operational failures. However, during atomization of water solutions this leads to the fact that in inoperative condition air originally present in the pump is driven out slowly and not completely and is replaced by the liquid, since the air partially deposits on the inner surfaces of the pump in form of small bubbles. The air bubbles located inside the pressure chamber of the pump are compressed during operation of the pump and the pressure increase in the respective interior of the pump chamber connected therewith, reduce their volume and lead to an idle stroke which is not a fluid output and is increased as compared with the normal idle stroke. Therefore, simultaneously a decrease of the output relative to the nominal output takes place.
During the return stroke of the pump piston, the air bubbles expand and thereby reduce the aspiration quantity of the pump. The thus produced deviation from the proper nominal output is not constant from stroke to stroke or from pump to pump, but instead varies in a wide range with differences of the order of approximately 50%. After a high number of strokes, for example at most more than 100 strokes, the air portion is removed from the pump so that the effective output can be equal to the nominal output in sufficient value. However, in many cases air collected prior to the inlet valve is released from there and travels into the pressure chamber and to again reduce the output. Such an uncontrolled condition is not tolerable in the case of utilization of the pump in pharmaceutical field, where it is necessary to provide constantly accurate output which is constant from stroke to stroke.